Snowden stole `keys to the kingdom`: NSA

US intelligence leaker Edward Snowden effectively stole the "keys to the kingdom" when he swiped more than 1.5 million top secret files, a senior National Security Agency official said in an interview.

Washington: US intelligence leaker Edward Snowden effectively stole the "keys to the kingdom" when he swiped more than 1.5 million top secret files, a senior National Security Agency official said in an interview.

Rick Ledgett, who heads the NSA taskforce in charge of assessing the impact of Snowden`s leaks, told CBS televisions`s "60 Minutes" aired yesterday that the contractor possessed a "roadmap" of the US intelligence community`s strengths and weaknesses.

NSA chief General Keith Alexander meanwhile said that suggestions the agency was routinely eavesdropping on the phone calls of Americans was false, insisting that less than 60 "US persons" were currently being targeted worldwide.

Ledgett said of particular concern was Snowden`s theft of around 31,000 documents the NSA official described as an "exhaustive list of the requirements that have been levied against the National Security Agency."

"What that gives is, what topics we`re interested in, where our gaps are," said Ledgett. "Additional information about US capabilities and US gaps is provided as part of that."

The information could potentially offer a rival nation a "roadmap of what we know, what we don`t know, and give them -- implicitly -- a way to protect their information from the US intelligence community`s view," the NSA official added.

"It is the keys to the kingdom."

Ledgett said he would be open to the possibility of an amnesty for Snowden, who remains exiled in Russia, if he agreed to stop further leaks of classified information.